Electron discharge device



March 2, 1.943..` F. B. LLEwk-:LLYN 2,312,723

ELECTRON DISCHARGE DEVICE Filed Aug. 1e, 1939 5 sheetssneet 1 //vEA/TonE B. LLEWELLV/V ATTORNEY F. B. LLEWELLYN 2,312,723

ELECTRON DISCHARGE DEVICE I Filed Aug. 16, 1939 s sheets-sheet 2/NVENTOR E ELLEWELLVN er A T TORNE Y March 2, 1943. F. B. LLEWELLYNELEQTRON DI'SCHARGE DEVICE Filed Aug.. 1e, 1559 s sheets-shea :s

/A/vE/vron BVEB. LLEWELLYN Patented Mar. 2, 1943 ELECTRON DISCHARGEDEVICE Application August 16, 1939, Serial Nc. 290,387

` v(ci. 25o- 36) 14 Claims.

The present invention relates to ultra-high frequency circuits employingelectronic apparatus for amplification or oscillation production andmore particularly to those types of such apparatus which utilize astream of electrons as may be obtained from what is commonly termed anelectron gun.

A principal object of the invention is to provide in ultra-highfrequency generating and amplifying apparatus an electron stream of highcurrent intensity to permit relatively high power operation.

Another object is to prevent dispersion of electrons along the path ofthe stream thereby avoiding losses due to some of them striking variouselements of the apparatus.

Another object is to produce a convergent or divergent field for suchpropagation of an electron stream.

Another object is to provide means for controlling the eld in theimmediate vicinity of an electron emitting cathode located in the eld ofan accelerating electrode so that the electrons may be drawn from theemitter in either a parallel, convergent or divergent stream.

A further object is to provide in a split plate type of magnetrongenerator an electric field which will project electrons divergently inradial directions from a point cathode at one end of the plate, thusavoiding the necessity for a cathode between the plates which would besusceptible to bombardment, and then carry them axially toward acollector thus avoiding congestion of electrons in the space between theplates.

In many circuits utilizing electron discharge tubes there is need forprojecting an electron stream of high current intensity over arelatively long path and diiculties are encountered both in initiatingsuch a stream and in avoiding energy loss through the dispersion ofelectrons along its path. These difficulties are minimized vaccording tothis invention through the use of a longitudinal accelerating fieldproduced by a form of electrode which surrounds the electron path anddistributes the eld producing potentials advantageously with respect toit. It is to be understood in this specification and the appended claimsthat the term accelerating or variations of it, when used withoutqualification may refer to either positive or negative acceleration andthat the qualications positive and negative are to indicate that theaccelerating force is applied to the electrons in the direction awayfrom the emitter and in the opposite direction respectively. Theelectrode may be connected to either positively accelerate, that is,increase the velocity of a stream of electrons away from the emitter orto negatively accelerate, that is, decrease the velocity away from theemitter or reverse the direction of a stream of electrons. A typicalelectrode achieving 'the desired result consists of tWo parts ofconducting material insulated from each other and maintained atdifferent potentials according to the intensity of the electric fielddesired. E ach part may be either integral or made up' of a multiplicityof elements properly insulated and interconnected, the essential featurebeing that the portions of each part effective in producing the eld bedisposed around the axis of the electron path and along the axis in sucha manner that the effective amounts of material at the two diierentpotentials preponderate at diierent ends of the electrode enclosingspace and extend in decreasing amounts and interspersed with each otherto 'the opposite ends. Since the electric eld at any point is producedby the resultant effect of the adjacent portions of the two parts of theelectrode which are at diierent potentials it will be seen that thefield will vary along the axis of the electrode in accord with therelative amounts of the eifective material at each potential. Thepotential of the field will ,be greatest at one end of the electrode,and

least at the other end with intermediate values in between. When theparts of the electrode are placed symmetrically around the axis theplanes at right angles to the axis will be equipotential at all pointsalong the electrode. An electrode may be made up of more than two partsand energized with more than one potential difference or severalelectrodes may be placed in tandem to extend the length of the enclosedelectron path or Yto obtain a eld of higher potential difference.

An electric eld of the type thus produced is particularly adapted toextracting electrons in a parallel beam from a cathode placed Within itand to maintaining the beam parallel over an extended length of path.This property is of value in connection with the generation and controlof ultra-high frequency power. It is of particular value in theapplication of electron guns to the generation of high frequency powersuch as Where an electron stream is sent through a iield associated withan electrically resonant chamber or circuit as referred to in mycopending application Serial No. 156,647 filed July 31,

15387, patented February 20, 1940, Patent No.

2,190,668, or when what is sometimes referred to as velocity modulationis employed, where the electron stream is subjected to different fieldconditions in different parts of its path as shown in my prior PatentNo. 2,096,460 issued October 3.9, 1937. This velocity modulation processis discussed quite extensively in an article by Messrs. W. C. Hahn andG. F. Metcalf in the Proceedings of the Institute of Radio Engineers,vol. 27, February 1939, pages 110 to 116, and is touched upon briefly ina note by R. H. Varian and S. F. Varian in the Journal of AppliedPhysics, vol. 10, February 1939, page 140.

Several possible variations of the electrode structure are shownincluding structures to produce convergent or divergent as well asparallel electron beams. Amplifier and oscillator circuits and anarrangement for excitation of a wave guide all adapted to use of theparallel electron beam are shown and also the application of a beamdivergent at the cathode to a split plate magnetron employing in theplate the composite electrode structure.

The various features of the invention will be more fully understood fromthe following detailed description of the illustrative embodime-ntsshown in the accompanying drawings.

In the drawings:

Figs. 1, 2 and 3 illustrate a method oi fabricating a compositeelectrode, cylindrical in form, to produce the desired type of parallelaccelerating eld;

Fig. 4 indicates the nature of the electric field within the cylindricalelectrode of Fig. 3;

Fig. 5 is a development of a section of the cylindrical electrode ofFig. 3 to indicate more clearly the relations of the elements;

Figs. 6 and 7 show variations in the element of Fig. 2 to produce eitherconvergent or divergent fields;

Figs. 8 and 9 show an alternative to the method of construction shown inFigs. 1, 2, 3 and 5;

Fig. 10 shows an electron gun employing the composite electrode toproduce the desired type of accelerating eld and means for controllingthe character of the electron stream as it leaves the cathode;

Fig. 11 shows the axial section of a resonant chamber such as a shortsection of cylindrical wave guide arranged for excitation by an electrongun of the type shown in Fig. 10 and connection to a wave guide fortransmission of the high frequency energy;

Fig. 12 shows a transverse section of a cylindrical wave guide arrangedfor direct excitation by an electron gun of the type shown in Fig. 10;

Fig. 13 shows an ultra-high frequency ampliiier circuit utilizingcomposite electrodes and resonant cavities as circuit elements;

Fig. 14 shows a modification of Fig. 13 to convert it to an oscillatorcircuit;

Fig. 15 shows an adaptation of the composite electrode structure to atype oi split plate magnetron; and

Fig. 16 shows a tandem arrangement of composite electrodes in anelectron gun and also a composite decelerating electrode.

In Figs. 1, 2 and 3 which show one method of constructing a compositeelectrode for producing a compact uniform accelerating field the twoessential parts, I and 2, are indicated in Fig. 1 and Fig. 2. In Fig. 1is represented a tube, If. which is composed of conducting material andforms the outer element of the composite electrode. In Fig. 2 is shownanother tube, 2, of conducting material which has been cut in the formof a crown. In the assembly, the tube 2 is inserted inside of I but insuch a way that electrical contact between the two conducting surfacesis avoided. One way of accomplishing this is to coat'the outside of thecrown 2 with an insulating material. For example, if 2 is made ofaluminum, it may be processed to form aluminum oxide on the outersurface. Another method is to dip the crown into molten glass to providea thin coating, taking care that the inner surface is clean ofdielectric. Yet a third method is to employ vacuum dielectric, mountingthe crown within the tube I in such a way that a thin insulating spaceis maintained. Whichever method is used, the assembly is shown in Fig. 3where the points of the crown are just visible in the perspectivedrawing. In operation, the two tubes I and 2, respectively, are biasedto diierent potentials. For example, suppose that I be placed at voltsand 2 at zero. The resulting field distribution is shown in Fig. 4. Itsform may be derived from the following considerations. At the top of theassembly, Fig. 3, the potential is evidently the same as that of theouter tube I, namely 100 volts. This is because the periphery of theassembled electrode at the top is composed entirely of material I at 100volts. On the other hand the potential at the bottom of the assembly isevidently that of the inner crown 2 because the material forming 2completely covers that of I at the lower edge of the assembly. Thepotential at that plane is thus the same as of 2, namely zero. Thisrelation of the parts may be more evident from an inspection of Fig. 5which is a development of a portion of the assembly Fig. 3 showing onlymaterial of cylinder I exposed inwardly at X, the top or 100 voltpotential end of the electrode, and only material of the crown 2 exposedinwardly at Y, the bottom or zero potential end of the electrode. InFig. 5 the thicknesses of the materials are exaggerated for clearness.Since at intermediate points along the axis portions of both materialsare exposed in wardly, planes at intermediate points perpendicular tothe axis will form equipotential surfaces intermediate between zero and100 volts, and the lines of force are, therefore, distributed along theaxis of the cylinder as shown in Fig. 4. Close to the periphery of thecylinder, the lines of force are distorted because of the striated formof the walls. But, provided these striations are small in size comparedwith the radius of the tube, the distorted iield penetrates only a smallway into the interior of the cylinder. As a matter of practicalconstruction, the striations do not need to be much smaller than thedistance between the periphery and the outer surface of the electronbeam which it is intended shall pass through in order that the fieldacting on the electrons in the beam shall be substantially axial. Ananalysis indicating the uniformity of the field from such a compositeelectrode is given in a copending application of Frank Gray, Serial No.290,359, filed August 16, 1939'.

Modications of the structure shown in Figs. 1, 2 and 3 to provide fieldswhich will cause the electron beam to converge or diverge are indicatedin Figs. 6 and 7 which show crown-shaped parts corresponding to 2 ofFig. 2, for electrodes to produce converging, or divergingbeams'respectively. The part I, Fig. 1, would necessarily be taperedalso to fit the desired tapered part 2 shown in either Fig. 6 or Fig. 7.

An alternative form of constructing the cornposite electrode is shown inFigs. 8 and 9. Instead of the inner electrode being formed in the shapeof a crown as shown in Fig. 2, a tapered strip of conducting material 2,Fig. 8, insulated on one side, is'wound inside of an outer conductingcylinder I, Fig. 9, similar to I, Fig. 1, so that the assembly willappear as in Fig. 9, which is a section through the axis of revolution.It is seen that here also the relative amounts of the two materialsexposed vary from end to end of the electrode which will vary theelectric eld along the axis accordingly. This construction has theadvantage that the distorting striations near the walls of the tube areof such a nature that they tend to prevent any electrons which aremoving near the wall from hitting it, and thus lfend to decrease straycurrents to the electrode. In constructing the electrode of Fig. 9, onemethod is to wind the tapered strip upon a mandrel and then cut theouter tube in two parts by a sawcut through its axis. The two halves ofthe outer tube may then be placed over the tape on the mandrel, andfastened in place, after which the mandrel may be removed.

Fig. l() shows an electron gun suitable for many uses including theapplications indicated above utilizing a composite electrode for thepurpose of extracting electrons from a cathode and projecting them inthe form of a parallel beam along a path determined by the axis of thegun. In this gure an evacuated tube 3 contains a cathode 4 the emittingsurface of which is disposed substantially perpendicular to the axis ofthe desired electron beam, composite positively accelerating electrode5, auxiliary accelerating electrode and collector plate l. The compositeelectrode 5, which is indicated for illustration to be of theconstruction shown in Fig. 3, surrounds the cathode 4 which is thesource of electrons. The cathode 4 is normally biased by means ofbattery 8, or equivalent, to a potential near that of the space adjacentto it as determined by the electrode 5, so that the electrons areextracted in a parallel beam. However, a focussing effect maybe had bybiasing the cathode to a potential slightly different from that of thesurrounding space. For example, if the cathode potential is lower than.that of the space the equipotential surfaces will be dish-shaped insteadof fiat in the vicinity of the cathode and the lines of force will causethe electrons to diverge leaving thecathode.v Conversely, if the cathodepotential is higher than that of the space the electrons will convergeleaving. the cathode. In order to control desirably the structureof theelectron stream in this manner the source of biasing potential 9 isconveniently made adjustable. The cross-sectional area of the beam maybe somewhat controlled since the biasing of the cathode curves theequipotential surfaces only in the immediate vicinity of the cathode andthe beam becomes substantially parallel further on in the compositeelectrode after having' converged or diverged over a short distance justafter leaving the cathode. A cathode heating source is indicated bybattery 3.

The composite electrode is shown polarized by battery IG which isconnected to the two parts of the electrode so that the partpreponderating more distant from the cathode, terminal I4, is the morepositive in order tolextract electrons from the cathode and project themtoward the collector 1. The terminal of the part preponderating nearerthe cathode is indicated at I3 and is connected to the negative terminalof battery It. Subsequent to the composite electrode 5 in the path ofthe beam a high potential accelerating electrode 6, energized by batteryII, is'v shown which may be employed if desired to further acceleratethe electron stream.' After the electron stream has delivered energy toa high frequency field the spent electrons may be collected atrelatively low potential at collector 'Ifand returned to the cathode.

:.Fig. 11 shows the electron gun of Fig. 10 adapted to the excitation ofa short section of wave guide and a method of transferring the highfrequency energy generated therein for transmission through a waveguide. The electron gun 3 is inserted along the axis through the shortsection of wave guide I5 which constitutes the resonant cavity describedin my Patent 2,190,668 and shown in Fig. l0 therein. The stream ofelectrons Will react with the type of electric eld Within the section ofguide which consists of symmetric longitudinal loops with the lines ofelectric force passing along the axis and along the enclosing conductorof the guide and this type of wave will be produced by the electronswhen their transit time is equal to the period of 11A, 21/4, 31A, etc.,cycles of the high frequency as explained in the above-mentionedcopending application. The coaxial line consisting of the outerconductor I l and the inner conductor I8 is shown arranged to transferthe high frequency energy in such a wave to the Wave guide I9 by virtueof the inner conductor I8 projecting into both sections of guides in amanner to couple with the electric fields. The small projectingcylinders I6, I6 placed at the openings through which the 'electron gunis inserted are to prevent loss through radiation through thoseopenings, the cylinders being made of sufficiently small diameter thatthe frequency of the energy within the guide is too low for them totransmit acting as wave guides.

Since the output and efficiency of a high frequency generator ofv thistype depends so greatly upon the intensity and definition of theelectron stream the use, as here shown, of the composite electrode 5which is capable of extracting from the cathode and projecting aparallel electron beam of high energy content greatly facilitates theproduction and transmission of a relatively large amount of highfrequency energy.

Another method of utilizing the electron gun of Fig. v10 to produce highfrequency waves in a Wave guide is shown in Fig. 12. Here the electrongun is shown passing transversely through the cylindrical Wave guide I5.The small projecting cylinders I6, I6 are placed at the openings of thewave guide to prevent loss through radiationas explained in connectionwith Fig. 11. The components of the electron gun and the connections toit are the same as shown in Fig. 10 and here again the high voltageaccelerating electrode 6 may be used or not as requirements indicate. Itis apparent that the stream of electrons passing transversely throughthe cylindrical guide is capable of reacting with a type of electric eldWithin the guide which consists oi' asymmetric loops with the lines ofelectric force passing transverse to the axis and around the two halves.of the enclosing conductor in'oppou site 'directions and this type ofwave will be produced by the electrons when their transit time i:

Tas indicated above in connectionl with Fig` 11.

The arrangement of Fig. 12 is quite similar to that of Fig. 14 of mycopending application Serial No. 156,647 referred to above in that theportion of the wave guide immediately surrounding the electron gun mustbe closed 01T to the proper length with a plunger and an iris diaphragmto determine the frequency and extent of radiation as indicated in thatapplication and shown in the associated Fig. 14.

Another application of the composite electrode to the problem ofprojecting a high energy electron beam is shown in Figs. 13 and 14representing a high frequency amplifier and oscillator circuit utilizingthe principle of velocity modulation, which, as previously mentioned, isdescribed in considerable detail by Messrs. Hahn and Metcalf in theProceedings of the Institute of Radio 'Engineers, vol. 27, February1939, pages 110 to 116 and is also referred to in an application of itdescribed by Messrs. R. H. Varian and S. F. Varian in the Journal ofApplied Physics, Vol. l0, February 1939, page 140. In Fig. 13, A is aresonant cavity of the circular reentrant type which serves as the inputcircuit and may be coupled to an input line as shown. B is a similarresonant cavity serving in a similar manner as the output circuit. Thecathode heated by battery 8 is located within the composite electrodewhich is energized by battery l0. The electrode 5 and cathode 4 areoperated in the manner described in connection with Fig. to project astream of electrons through the fields of A and B at 2l and 22,respectively, and the cathode is biased by means of battery 9 to obtainthe proper shape of emission as described in connection with Fig. 10. Asecond composite electrode 6, energized by battery l l and a thirdelectrode 23, energized by battery 25, which may or may not be of thecomposite type direct the electrons through to the electrode l,energized by battery I2, where they are collected. Terminal of 6, andterminal I4 of 5, are the connections to the parts of the respectiveelectrodes which preponderate farther from the cathode and are madepositive relative to terminals 2d of 6 and I3 of 5, respectively, whichare the connections to the parts of the respective electrodes whichpreponderate nearer to the cathode. The arrangement shown in Fig. 13, isthat of an amplifier with input and output connec-tions as indicated.The electron stream from the cathode 4 to the collector 'I passesthrough the electric eld of cavity A for a short distance at 2i andthrough the eld of cavity B for a short distance at 22. The alternatingfield at 2i due to the current in A which is derived from the input tothe amplier reacts upon the electron stream to speed up those electronswhich enter the eld during one half of each cycle and to retard thosewhich enter during the other half cycles. After leaving the region ofthe field at 2| the electrons which have had their velocity increasedtend to overtake those which have had their velocity reduced so that bythe time the region of the field at 22 is reached a rearrangement of theelectrons along the stream has taken place and the stream is no longerof uniform density. v Regions of greater and less electron densityalternate in accordance with the effect of the field at 2l. In otherwords, the electron stream has been density modulated in accordance withthe rinput lto the amplier. Now in passing through the region 22 ofcavity B the variations in the density of the electron stream willinduce a varying current in B proportional to the input to A and,- ofcourse, of the same frequency, so

that the inputhigh frequency energy is amplified and deliveredthrough-the output line coupled to B. The alternating eld produced at 22by the current in B Will oppose the passage of the electrons and reducetheir velocities, the spent electrons are removed from the vicinity ofregion 22 by the electrode 23 and collected at relatively low potentialby the collector 7. As with any amplifier, this circuit may be readilymodified to act as an oscillator by coupling a portion of the outputenergy to the input. A method of doing this is shown in Fig. 14. Acoaxial line 21 couples the two cavities A and B in order to excite theinput circuit A with energy from B. The line 21 must be of such lengthand the electron transit time between points 2| and 22 such that thecurrents in A and B are in proper phase relation to cooperate insustaining oscillations.

Another application of the composite electrode structure is illustratedin Fig. 15 which shows the active elements of a split plate magnetron inwhich the split plate 5 is of composite construction. The form ofconstruction shown is that of Fig. 3 though alternative forms will serveequally well. An axial magnetic field indicated by I-I secured by meansof coil 28 is employed. The source of electrons is the cathode 4 whichin vthis case is biased below the potential of its surrounding space sothat the electrons are drawn orf sharply diverging in radial directionsas explained in connection with the description of Fig. 10 wherereference is made to the focusing effect of biasing the cathode to apotential different from that of the surrounding space. The elec- 5trons spiral at approximately right angles to the axis between the axisand the plate and deliver energy to the alternating field existingbetween the split in the plate thus delivering energy to the circuitincluding the plate and to the output circuit 29. The output circuitwhich is indicated at 29 may be of any desired form which will couplevwith the alternating field of the magnetron when placed in proximity toit. As an alternative, direct connection may be made to the plate of themagnetron at appropriate points such as C and D, the position along theplate, assuming the magnetron elements are not part of an external tunedcircuit, being determined by the impedance of the load circuit to beattached. The longitudinal electric field of the composite plate 5 movesthe spiraling electrons axially toward electrode 'l where they may becollected at relatively low potential. For very high frequency operationit is convenient to make the split plate 1A; wave-length long the partsbeing connected together at the cathode end as shown in Fig. 15. Forlower frequency use it is desirable to have no internal high frequencyconnection between the parts of the plate and to make them part of anexternal tuned circuit. The connection of battery I9 is such that thepositive terminal is connected to the external portion of the plate,corresponding to i of Figs. 1 and 3, and the negative terminal is.connected to the inner crown-shaped member, corresponding to 2 of Figs.2 and 3, which must be insulated from the external portion for thedirect voltage of l0 and must be split longitudinally the same as theouter portion as shown in Fig. 15. The most positive end of the field ofthe composite structure due to the potential of battery l0 is in thedirection toward collector 1 from the cathode 4. The battery 9 is forthe purpose of biasing the cathode '4 below the surrounding spacepotential in order to obtain the radially divergent stream of electronsfrom the cathode. It will be seen that this structure is free from anyobstruction, such as a cathode, within the splitplate cylinder and alongits axis which may be bombarded by moving electrons entailing energyloss and damage and also that the longitudinal field due to thecomposite electrode structure of the split plate will electively clearthe space between the plates of spent electrons.

Fig. 16 is similar to Fig. 10 and shows some alternative arrangements ofcomposite electrodes in the electron gun of Fig. 10. An additionalcomposite positively accelerating electrode 30 which is energized bysource 3| is shown in tandem with electrode 5. As mentioned previously anumber of composite electrodes may be placed in tandem to obtain higherpotential accelerating fields. The auxiliary electrode 6 may or may notbe used as the requirements of the application indicate. Electrode 32 isshown to illustrate the use of `a composite negatively acceleratingelectrode. It is constructed the same as a positively acceleratingelectrode such as 5, but is connected to its source of potential 33 sothat its more positive end is directed toward the emitter and away fromthe collector 'I to that its eld will tend to retard the electronsbefore they strike the collector thereby minimizing the energy to bedissipated in the form of heat at the collector. In general, in thevarious applications of the electron gun illustrated, where the gun ofFig. 10 is shown or referred to the gun of Fig. 16 or some other similarmodification of the Fig. 10 arrangement may be substituted. Any of thecomposite electrode structures shown may be connected with respect topolarity to give either positive or negative acceleration to theelectron stream and to any of the utilization circuits shown one or morenegatively accelerating electrodes may be added to retard or reverse theelectron stream.

With the examples that have been given of forms of embodiment, variousmodifications for use of the composite electrode in electron gunapplications will naturally suggest themselves to those skilled in theart and it is intended that the invention is not to be limited to thespecific forms disclosed but only by the scope of th claims. Y

What is claimed is:

1. In combination, a space discharge tube comprising an electronemitter, a positively accelerating electrode surrounding the path ofelectron discharge for at least a portion of its length and also theelectron emitter in directions perpendicular to the path, the saidaccelerating electrode being of composite construction composed of twoconducting elements insulated from each other and with those portions ofthe surfaces of the elements which are directly exposed to the pathcommingled so that the combined surface which is exposed to the electronstream, and thus capable of affecting it, varies along the direction ofthe path from being substantially entirely of one element at one placeto being substantially entirely of the other element at another while inbetween the combined exposed surface is a mixture of the two elementsthe portion of each diminishing in the direction of where the otherpreponderates, and an electron collector at the end of the dischargepath, means for maintaining the elements of the composite positivelyaccelerating electrodeat different potentials such that the elementwhich preponderates `farthest from the electron emitter is morepositive, means for maintaining the electron collector at a positivepotential With respect to the emitter and a resonant cavity surroundingat least a Iportion of the tube and through which the electron pathextends wherein by virtue of the critical relation between the operatingfrequency and the transit time of the electrons through the cavityenergy is transferred from the electron stream to the cavity.

2. In an oscillation generating circuit an electron discharge tubecomprising an electron emitting cathode, a plurality of platessurrounding and extending along an axisA including the cathode, thecathode being located between and near one end of the plates, the platesbeing insulated from each other throughout portions of their length,each plate being composed of two conducting elements insulated from eachother and with those portions of the surfaces of the elements which areexposed directly to the aforementioned axis commingled so that thecombined surfaceof each plate exposed to the axis varies along thedirection of the axis from being substantially entirely of one elementat one end of the plate to ,being substantially entirely of the otherelement at the other end while in between the combined exposed surfaceis a mixture of the two elements, the portion of each diminishing in thedirection of the end where the other preponderates, means formaintaining the two elements of each plate at different potentials suchthat the element which preponderates farthest from the cathode is morepositive, means for maintaining the cathode at a potential lower thanthat of the space in the transverse plane including the cathode which isproduced by the potentials of the plates, means for maintaining amagnetic field parallel to the axis and in the direction of the platesaway from the cathode, an electron collector at the end of the platesopposite the cathode, means for maintaining the collector positive withrespect to the cathode and an output circuit coupled to the plates.

3. In an electron discharge device, an accelerating electrodesurrounding at least a portion of the discharge path utilizing twoconcentric elements of conducting material, one fitting inside of theother and insulated from each other so that a difference of potentialmay be maintained between them, the internal element being so formedthat the amount by which it covers or shields from within the interiorsurface of the outer element varies from one end of the electrode to theother.

4. In combination, a source of electrons, a tubular conducting membersurrounding the path of electron discharge for at least a portion of itslength and another member insulated from the rst member and positionedwithin it to overlap portions of its inner surface as viewed from theelectron stream, means for impressing an electromotive force between thetwo members, the inner member having openings to expose the electronstream to the field of the outer member, the areas of the openingsincreasing progressively with distance from one end of the assembly tothe other so that the resultant electric eld in which the electrons aremoving is substantially uniform.

5. In an electron discharge device an eccelerating electrode surroundingat least a portion of the discharge path utilizing two concentricelements of conducting material, one fitting inside of the other 'andinsulated from each other so that a difference of potential may bemaintained between them, the' external element having a complete tubularsurface, the inner element being deeply serrated on one end as if madeup of tapered or triangular elements with the bases contiguous at oneend and the points or apexes separated at the other end so that thecuter element is completely covered or shielded at the end where thebases are positioned and completely uncovered or unshielded at the endwhere the points or apexes are positioned.

6. In combination, an electron emitter and an accelerating electrodeconsisting of at least two series of commingled but non-overlappingareas of conducting members surrounding the electron emitter and thepath of discharge of emitted electrons in directions perpendicular tothe said path, the series being insulated from each other and subjectedto different potentials to produce a joint substantially uniformelectric field in which the electrons are accelerated, and means toimpress a potential upon the electron emitter positive with respect tothat of the virtual potential of the accelerating electrode in the planeincluding the emitter so as to tend to focus the electron dischargebeam.

'7. The combination according to claim 6 in which the voltage impressedupon the electron emitter is negative with respect to that of thevirtual potential of the accelerating electrode in the plane includingthe emitter so as to tend to diverge the electron discharge beam.

3. The combination according to claim 6 in which the Voltage impressedupon the electron emitter is the same or slightly different from thevirtual potential of the accelerating electrode in the plane includingthe emitter so as to tend to maintain the parallelism of the electrondischarge beam.

9. An electric wave transmission apparatus comprising an electrondischarge device having a source of electrons, an anode and a controlelement interposed between the electron source and the anode andsurrounding the path of electron discharge for at least a portion ofitslength and also the electron source in directions perpendicular tothe path, the control element comprising two conducting membersinsulated from each other and having such conformation that the surfaceexposure to the electron stream of one member increases along theelectron stream as the surface exposure of the other member to thestream decreases, means for polarizing the two members of the controlelement at dierent potentials with respect to the electron sourcewhereby the stream of electrons emanating from the electron source isaccelerated uniformly within a given zone to produce a high intensityelectron stream, means for polarizing the anode positively with respectto the cathode, the conducting members of the control element beingdivided longitudinally throughout most of their length except for aconnection at one end to constitute an electrically resonant circuitcomprising conducting surfaces symmetrically positioned with respect tothe electron stream to set up an electromagnetic iield through which theelectron stream passes whereby upon reaction between the electromagneticfield and the high intensity electron stream a large energy transferoccurs from the stream to the electromagnetic field and means forwithdrawing wave energy from the electromagnetic eld.

10. A space discharge device comprising an electron emitting cathode, ananode, means for polarizing the anode positively with respect to thecathode, a control: electrode interposed between the cathode and anodeand surrounding the path of electron discharge for atleast a portion ofits length including its point of origin at the cathode, the controlelectrode serving to accelerate electrons uniformly within a given zoneand comprising two conducting members insulated from each other andhaving such conformation that the surface exposure of one memberincreases along the electron stream as the surface exposure of the othermember to the stream decreases and means for polarizing the two membersat different potentials with respect to each other and to the cathode,means for producing high frequency variations in the electron stream, anoutput circuit and means responsive to high frequency variations in theelectron stream for transferring energy therefrom to the output circuit.

l1. An electric wave transmission apparatus comprising an electrondischarge device having a source of electrons,`an anode and a controlelement interposed between the electron source and the anode andsurrounding the path of electron discharge for at least a portion of itslength including its place of origin at the electron source, the controlelement comprising two conducting members insulated from each other andhaving such conformation that the surface exposure to the electronstream of one member increases along the electron stream as .the surfaceexposure of the other member to the stream decreases, means. forpolarizing the two members of the control element at differentpotentials with respect to the electron source whereby the stream ofelectrons emanating from the electron source is accelerated uniformlywithin a given zone to produce a high intensity electron stream, meansfor polarizing the anode positively with respect to the cathode, meansfor setting up an alternating electromagnetic eld in a zone throughwhich the electron stream passes whereby upon reaction between theelectromagnetic field and the high intensity electron stream a largeenergy transfer occurs from the stream to the electromagnetic field andmeansA for withdrawing wave energy from the electromagnetic field.

12. In combination, a space discharge tube comprising an electronemitter, a positively accelerating electrode surrounding the path ofelectron discharge for at least a portion of its length and also theelectron emitter in directions perpendicular to the said pathvandbeingof composite construction composed of two conducting elements insulatedfrom each other and,l with those portions of the surfaces of theelements which are directly exposed to the path commingled so that thecombinedA surface which, is exposed to the electron stream, and thusCapable of affecting it, varies along the direction of the path frombeing substantially enti-rely of one, e1e. ment at one place to beingYsubstantially entirely of the other element atanother while between thecombined exposed surface is a mixture of the two elements `the portionof each diminishing in the direction of where the other preponderates,and an electron collector at` the end of the dise'v charge path, meansfor maintaining the elements of the composite positively acceleratingelectrode at different potentials such that the` element whichpreponderates farthestv from the electronV emitter is more positive,means for maintaining the electron collector at a` positive potentialwith respect to the emitter and a, resonant cavity sur,- rounding atleast a portion of theV tube and through which the electron path extendswherein by virtue of the critical relation between the voperatingfrequency and the transit time of the electrons through the cavityenergy is transferred from the electron stream to the cavity.

13. An amplier circuit comprising an electron discharge tube having anelectron emitting cathode, a positively accelerating electrodesurrounding a portion of the electron discharge path and also theemitting portion of the cathode in directions perpendicular to the saidpath, the said accelerating electron being of composite construction,composed of two conducting elements insulated from each other and withthose portions of the surfaces of the elements which are directlyexposed to the path commingled so that the combined surface which isexposed to the electron stream, and thus capable of affecting it, variesalong the direction of the path from being substantially entirely of oneelement at one place to being substantially entirely of the otherelement at another while in between the combined exposed surface is amixture of the two elements the portion of each diminishing in thedirection of Where the other preponderates and a collecting electrode atthe end of the electron path, means for maintaining the elements of thecomposite positively accelerating electrode at diierent potentials suchthat the element which preponderates farthest from the electron emitteris more positive, means for maintaining the collector at a positivepotential With respect to the cathode, a cavity resonator positionedaround the tube such that the electron stream passes through its field,an input coupled to said resonator for the electrical excitationthereof, a second resonant cavity positioned around the tube furtheralong on the electron .path such that the electron stream passes throughits eld for the purpose of delivering energy to it and an output circuitcoupled to the second resonator.

14. In an 'electron discharge device, an accelerating electrodesurrounding the electron emitter and at least a portion of the dischargepath in directions perpendicular to the said path utilizing twoconcentric elements of conducting material, one tting inside of theother and insulated from each other so that a difference of potentialmay be maintained between them, the internal element being so formedthat the amount by which it covers or shields from Within the interiorsurface of the outer element Varies from one end of the electrode to theother.

FREDERICK B. LLEWELLYN.

